Overview
Fine Needle Aspiration Cytology (FNAC) is a minimally invasive diagnostic procedure widely used for evaluating palpable and non-palpable lesions. It involves using a thin, hollow needle (typically 22-25 gauge) to aspirate cellular material from masses or nodules for cytological examination. FNAC has become an essential first-line investigation in the evaluation of thyroid nodules, breast lumps, lymphadenopathy, and soft tissue masses.
FNAC offers several advantages including rapid diagnosis, cost-effectiveness, minimal patient discomfort, and low complication rates. With diagnostic accuracy rates ranging from 90-95% in experienced hands, FNAC helps guide clinical management decisions and can often obviate the need for more invasive surgical biopsies. The procedure is particularly valuable in resource-limited settings and for patients who are poor surgical candidates.
Learn more in our comprehensive RxDx Pathology Course
Indications
Evaluation of solitary thyroid nodules >1cm or smaller nodules with suspicious ultrasound features
Triple assessment of palpable breast lumps (clinical, imaging, and cytology)
Persistent enlarged lymph nodes to differentiate reactive, infective, or malignant causes
Evaluation of parotid and submandibular gland swellings
Initial assessment of superficial soft tissue tumors and cystic lesions
Image-guided FNAC for focal liver lesions when histology is required
Contraindications
Absolute Contraindications
Relative Contraindications
📋 Equipment Checklist
Check off items as you gather them:
Pre-procedure Preparation
Patient preparation includes obtaining informed consent, reviewing coagulation parameters if indicated, and positioning based on the lesion location. The skin over the target area should be cleaned with antiseptic solution. Local anesthesia is optional for superficial lesions but may be used for deeper aspirations. Ultrasound guidance should be arranged for non-palpable or deep-seated lesions.Step-by-Step Procedure
Step 1: Patient Positioning and Site Preparation
Position the patient comfortably with the target lesion easily accessible. For thyroid nodules, extend the neck with a pillow under the shoulders. For breast lesions, position supine or lateral decubitus. Clean the skin over the lesion with antiseptic solution in a circular motion, starting from the center and moving outward. Allow the antiseptic to dry completely.
⚠️ Common Mistakes to Avoid:
- Inadequate positioning leading to patient movement during procedure
- Not allowing antiseptic to dry, which can contaminate the specimen
💡 Pro Tip:
For anxious patients, explain each step as you perform it. This reduces anxiety and improves cooperation.
Step 2: Lesion Fixation
Using your non-dominant hand, immobilize the lesion between your fingers (for superficial lesions) or identify it with ultrasound guidance (for deep lesions). For mobile lesions like lymph nodes, fix them firmly against underlying structures. Maintain this fixation throughout the procedure to prevent the lesion from rolling away from the needle.
⚠️ Common Mistakes to Avoid:
- Inadequate fixation causing the lesion to move during aspiration
- Applying excessive pressure that distorts the lesion architecture
💡 Pro Tip:
For small mobile lymph nodes, try the "V-grip" technique - fix the node between your index and middle fingers.
Step 3: Needle Insertion
Hold the syringe like a pencil at a 45-90 degree angle to the skin. Insert the needle swiftly through the skin and into the lesion in one smooth motion. You may feel a change in resistance as the needle enters the lesion. For cystic lesions, you may see fluid entering the needle hub.
⚠️ Common Mistakes to Avoid:
- Hesitant insertion causing more pain and tissue trauma
- Inserting the needle too deep and passing through the lesion
💡 Pro Tip:
For thyroid nodules, insert perpendicular to the skin. For breast lesions, a tangential approach may be safer.
Step 4: Aspiration Technique
Once the needle is in the lesion, pull back the plunger to create negative pressure (10-15 mL mark). While maintaining suction, move the needle back and forth within the lesion (5-10 passes) in different directions to sample different areas. This "fanning" technique ensures adequate cellularity. The excursion should be small (2-3 mm) to stay within the lesion.
⚠️ Common Mistakes to Avoid:
- Excessive negative pressure causing bloody aspirates
- Too few passes resulting in inadequate cellularity
- Moving the needle too far and exiting the lesion
💡 Pro Tip:
For vascular organs like thyroid, use less negative pressure (5-10 mL) to minimize blood contamination.
Step 5: Release Pressure and Withdraw
Before withdrawing the needle, release the negative pressure completely by letting go of the plunger. This prevents aspiration of cells into the syringe and contamination with skin cells. Withdraw the needle swiftly in one motion. Immediately apply pressure to the puncture site with sterile gauze.
⚠️ Common Mistakes to Avoid:
- Withdrawing needle without releasing pressure, losing specimen in syringe
- Slow withdrawal causing more tissue trauma
💡 Pro Tip:
Count "1-2-3: Insert-Aspirate-Release" to remember the correct sequence.
Step 6: Specimen Processing
Detach the needle from the syringe and draw 5-10 mL of air. Reattach the needle and gently express the aspirated material onto labeled glass slides by pushing the plunger. Place a drop near the frosted end of the slide. For liquid specimens, place smaller drops on multiple slides.
⚠️ Common Mistakes to Avoid:
- Forceful expression causing cell trauma and spray artifact
- Placing too much material on one slide creating thick smears
💡 Pro Tip:
If no material is visible in the needle hub, rinse the needle with saline into a container for cell block preparation.
Step 7: Smear Preparation
Quickly place a second slide over the drop at a 45-degree angle and pull apart with a smooth, swift motion to create thin smears. For bloody specimens, use the "pull-apart" technique. For thick material, use the "squash" technique with gentle pressure. Work quickly to prevent air-drying if using alcohol fixation.
⚠️ Common Mistakes to Avoid:
- Applying too much pressure causing cell crushing
- Slow smearing causing air-drying artifacts
- Creating smears that are too thick to interpret
💡 Pro Tip:
Practice smear techniques on non-clinical material first. Good smears are crucial for accurate diagnosis.
Step 8: Fixation and Labeling
Immediately fix the smears by either immersing in 95% ethanol (wet fixation) or using spray fixative held 25-30 cm from the slide (air-dried for Romanowsky stains). Label slides with patient details, site, and date. For wet fixation, keep slides in fixative for at least 15 minutes before staining.
⚠️ Common Mistakes to Avoid:
- Delayed fixation causing air-drying artifacts in alcohol-fixed smears
- Spray fixative too close causing cell distortion
- Inadequate labeling leading to specimen mix-ups
💡 Pro Tip:
Prepare two sets of slides: alcohol-fixed for Papanicolaou stain and air-dried for May-Grünwald-Giemsa stain.
Master FNAC with RxDx
Access 100+ procedure videos and expert guidance with the RxDx app
Post-procedure Care
Post-procedure care involves applying pressure to the puncture site for 5-10 minutes to prevent hematoma formation. Patients should be observed for 15-30 minutes for any immediate complications. Instructions include keeping the site clean and dry for 24 hours, watching for signs of infection or excessive bleeding, and returning for results discussion. Most patients can resume normal activities immediately.Complications & Management
| Complication | Incidence | Signs | Management | Prevention |
|---|---|---|---|---|
| Hematoma | 1-2% | Swelling, discoloration at puncture site | Apply firm pressure for 10-15 minutes, ice pack, observation | Adequate pressure post-procedure, avoid multiple passes in vascular lesions |
| Vasovagal reaction | 0.5-1% | Dizziness, sweating, bradycardia, hypotension | Trendelenburg position, monitor vitals, IV fluids if severe | Perform procedure with patient lying down, calm environment |
| Infection | <0.1% | Erythema, warmth, purulent discharge after 24-48 hours | Antibiotics based on culture, local wound care | Strict aseptic technique, avoid aspirating through infected skin |
| Pneumothorax | 0.1% (lung/chest lesions) | Dyspnea, chest pain, decreased breath sounds | Chest X-ray, oxygen, chest tube if significant | Careful technique for chest wall lesions, avoid trans-pulmonary route |
| Needle tract seeding | <0.01% | Nodules along needle tract (weeks to months later) | Surgical excision of tract if occurs | Minimize number of passes, avoid FNAC in certain tumors (e.g., hepatocellular carcinoma in transplant candidates) |
Clinical Pearls
For thyroid nodules, the "non-aspiration" technique (using capillary action without suction) often yields less bloody samples with adequate cellularity.
Always prepare extra slides - you cannot go back to get more material if the initial smears are inadequate.
For cystic lesions, completely evacuate the fluid and re-aspirate any residual solid component for better diagnostic yield.
Rapid on-site evaluation (ROSE) by a cytopathologist significantly improves adequacy rates and reduces need for repeat procedures.
Document the number of passes, needle gauge used, and gross appearance of aspirate in your procedure note.
The quality of smear preparation is as important as the aspiration technique - poor smears from good aspirates lead to non-diagnostic results.
For suspected lymphoma, always save material in RPMI medium for flow cytometry in addition to routine smears.
References
- Paul P, Azad S, Agrawal S, Rao S, Chowdhury N. Systematic Review and Meta-Analysis of the Diagnostic Accuracy of the International Academy of Cytology Yokohama System for Reporting Breast Fine-Needle Aspiration Biopsy in Diagnosing Breast Cancer. Acta Cytol. 2023; 67(1):1-16. PMID: 36412573
- Hatami H, Samsami M, Movahedinia S, Salehi B, Movahedinia M, Ardeshir M. Comparison of fine-needle aspiration with fine-needle capillary cytology in thyroid nodules. Ann R Coll Surg Engl. 2023; 105(2):162-165. PMID: 35446712
- Ha HJ, Lee J, Kim DY, Kim JS, Shin MS, Noh I, Koh JS, Kim EJ, Lee SS. Utility and Limitations of Fine-Needle Aspiration Cytology in the Diagnosis of Lymphadenopathy. Diagnostics (Basel). 2023; 13(4):728. PMID: 36832214
- Pinto DG, Schmitt FC. Overcoming Pitfalls in Breast Fine-Needle Aspiration Cytology: A Practical Review. Acta Cytol. 2024; 68(3):206-218. PMID: 38861943